1. Field of Invention
The present invention pertains to the field of digital clocks. More particularly, this invention relates to a method and apparatus for extending a resolution of a clock.
2. Art Background
A wide variety of systems commonly include digital clocks. Such clocks may be used for a wide variety of timing functions in a system. One example of a timing function is to measure a time at which an event in the system occurs. Another example of a timing function is to synchronize or "trigger" an occurrence of an event at a particular time. The nature of the events depends on the particulars of the system.
In a control system, for example, the act of obtaining a data sample from a sensor is an event as is the act of applying a control value to an actuator. A digital clock may be used to measure the time at which the data sample is obtained from the sensor. In addition, a digital clock may be used to trigger the application of the control value to the actuator at a particular time.
A typical digital clock includes an oscillator and circuitry that generates digital time values in response to the oscillator. The circuitry that generates digital time values may be, for example, a counter that generates an updated time value every period or half period of the oscillator. Typically, the resolution of such a digital clock is limited by the frequency of its oscillator. For example, an oscillator that runs at 1 megahertz has a period of 1 microsecond and can generate an updated time value every 0.5 microseconds, thereby yielding a resolution of 0.5 microseconds. Such a digital clock could not reliably distinguish events that occur within 0.5 microseconds of each other and could not reliably synchronize events that are to occur within 0.5 microseconds of each other. This may limit the overall performance of the system.
One prior method of increasing the resolution of a digital clock is to increase the frequency of its oscillator. Unfortunately, an increased oscillator frequency usually increases power consumption. In addition, higher oscillator frequencies usually complicate the design of circuitry for the digital clock. Moreover, an oscillator is commonly shared with other components of a system, such as a processor, which may not be amenable to a higher oscillator frequency.